Numerical Simulation of Mechanical Compaction of Deepwater Shallow Sediments

摘要

To study the compaction law and overpressure evolution in deepwater shallow sediments,a large-strain compaction model that considers material nonlinearity and moving boundary is formulated.The model considers the dependence of permeability and material properties on void ratio.The modified Cam-Clay model is selected as the constitutive relations of the sediments,and the deactivation/reactivation method is used to capture the moving top surface during the deposition process.A one-dimensional model is used to study the compaction law of the shallow sediments.Results show that the settlement of the shallow sediments is large under their own weight during compaction.The void ratio decreases strictly with burial depth and decreases more quickly near the seafloor than in the deeper layers.The generation of abnormal pressure in the shallow flow sands is closely related to the compaction law of shallow sediments.The two main factors that affect the generation of overpressure in the sands are deposition rate and permeability of overlying clay sediments.Overpressure increases with an increase in deposition rate and a decrease in the permeability of the overlying clay sediment.Moreover,an upper limit for the overpressure exists.A two-dimensional model is used to study the differential compaction of the shallow sediments.The pore pressure will still increase due to the inflow of the pore fluid from the neighboring clay sediment even though the deposition process is interrupted.